Koi shika Dekinai yo

Highschool Teacher Umehara-sensei has been transferred from an all-boys to an girls highschool when he meets his former pupil now university student Hataoka Kei. They start meeting each other to drink together. Umehara-sensei feels a bit weird to drink with his former pupil. But how much weirder would he feel if he could know that Kei has an obsessive love for him to the point where he starts to take up stalking habits ...